Electromagnet with spring-retained armature structure



L. C. ANDERSON, JR., ETAL Sept. 1, 1964 ELECTROMAGNET WITHSPRING-RETAINED ARMATURE STRUCTURE INVENTORS LQUIS C. ANDERSON JR.

FIG. 3

ARTHUR A". HAGSTROM ATJ'ORNEY United States Patent 3,147,410ELECTROMAGNET WITH SPRING-RETAINED ARMAT STRUCTURE Louis C. Anderson,In, Arlington Heights, and Arthur A. Hagstrom, Hoffman Estates, Roselle,111., assignors to Teletype Corporation, Skokie, 111., a corporation ofDelaware Filed Oct. 17, 1962, Ser. No. 231,227 Claims. (Cl. 317-165)This invention relates to an electromagnet assembly and moreparticularly to the mechanical construction of an electromagnetassembly.

Heretofore, magnet assemblies have consisted of a relatively largenumber of expensive elements, adjustable with respect to one another inorder to accurately establish a small air gap between the armature andthe pole face of the magnet and to maintain this small air gap after alarge number of cycles of operation with attendant wear and consequentlooseness of elements.

Accordingly, an object of the invention is to provide a magnet assemblythat has no adjustable components and which has relatively few andinexpensive elements that are readily assembled and disassembled.

Another object of the invention is to provide a magnet assembly whereinthe moving armature element is biased into contact with its bearingsurface to take up any looseness therebetween that might occur due towear.

A further object of the invention is to provide an electromagnetassembly having a wide bearing surface for its armature over which todistribute the wear load thereby reducing the amount of wear normallyencountered in electromagnet assemblies.

A further object of the invention is to provide a small powerfulelectromagnet assembly having a small easily established, nonadjustableair gap between its armature and pole face and wherein a small movementof its armature is translatable into a large movement of extensionsoperable by the armature.

A feature of the invention is to provide a more compact magnet assemblyby disposing the armature extensions in openings provided between theelectromagnets coil and laminations.

A feature of the invention is the retaining of the shaft, about whicharmature pivots, in receiving slots for the shaft under the urging of aspring acting through the armature of the electromagnet assembly.

According to the preferred embodiment of the invention the magnetassembly is comprised of an upper frame member to which are secured thelaminations and coil of the electromagnet. The frame member has machinedtherein receiving slots for an armature pivot shaft, the slots beingmachined simultaneously in the same operation as the machining of theends of the laminations to form a pole face for the magnet. Thus, thewidth and depth of the slots are accurately maintained with respect tothe pole face on the magnet laminations since both the slots and thepole face are machined simultaneously in the same machining operation.To secure the armature pivot shaft within the ground slots, a flat platearmature has wide bearing surfaces spring urged into engagement with thearmature pivot shaft to retain the armature pivot shaft within themachined slots. Armature extensions are secured to the armature andextend the length of the electromagnet in the openings between the coiland laminations. The armature extensions provide a large amount ofmovement at their free ends for a relatively small amount of movement ofthe armature. 1

Other features and advantages of the invention will become apparent fromthe following detailed description when considered in conjunction withthe accompanying drawings wherein:

3,147,410 Patented Sept. 1, 1964 ice FIG. 1 is a side elevational viewof the magnet assembly according to the preferred embodiment of theinvention;

FIG. 2 is a plan view of the magnet assembly, and

FIG. 3 is an end view of the magnet assembly having a portion of anarmature broken away to show the curved end portions of the armatureextensions that are secured to the armature.

Referring now to FIG. 1, there is illustrated a magnet assembly 10 forgenerating large forces capable of operating instrumentalities such as atape reader of the type shown in the copending application of L. C.Anderson,

In, A. A. Hagstrom and R. A. Thienemann, Serial No. 231,199 filed ofeven date herewith.

The electromagnet assembly 10 has a plurality of sheet metal laminations11 of an E-shaped configuration secured together by a plurality ofrivets 12 to constitute a unitary core assembly 13. The central leg ofthe core assembly 13 supports a hollow plastic bobbin 14 upon which arewound the turns of wire that constitute an energizable coil 15 for theelectromagnet assembly 10. The coil 15 is adapted to be energized in theconventional manner and causes magnetic flux to be distributed throughthe legs of the E-shaped laminations 11 to attract a metallic armature20 against the end portions of the legs of the E-shaped laminations 11that constitute the pole face 22 of the electromagnet assembly 10.

The pole face 22 of the laminations is machined by grinding or millingto assure a flat pole face 22 that is square with the laminations 11and, simultaneously with the machining of the pole face 22, slots 25 aremachined in a magnet support frame 26 and the frame 26 is machinedsquare with the pole face 22. The same machine tool is used to machinethe pole face 22 and slots 25. As seen in FIG. 2 the magnet supportframe 26 is of the same general E-shaped configuration as thelaminations 11 which are secured thereto by the rivets 12. As seen inFIG. 1, the magnet support frame 26 has an upwardly directed,strengthening flange 27 running longitudinally of the laminations 11 andending in vertically rising portion 28; and as seen in FIGS. 2 and 3,the magnet support frame 26 has an identical vertical portion 28 on theside opposite that shown in FIG. 1.

Since the receiving slots 26 are machined simultaneously with machiningof the pole face 22, the receiving slots 26 are accurately located bothas to the height of the slot above the laminations and also as the depthof the slot relative to the pole face 22. Disposed within the receivingslots 25 is an armature pivot shaft 30 which serves as the pivot aboutwhich the armature 211 rotates when it is moving either toward or fromthe pole face 22. The armature 20 is a piece of flat plate material witha pair of spaced upstanding fingers 31 (FIG. 3) which are in engagementwith the cylindrical surface of the armature pivot shaft 30. As seen inFIG. 1 the fingers 31 extend upwardly from the armature 20 to engage thearmature pivot shaft 30 at a line of contact 32, and elongated slots 33in vertical cars 34 on a pair of armature extensions 35 contact thearmature pivot shaft 30 at an upper point of contact 36 and a lowerpoint of contact 37. The armature extensions 35 terminate in inwardlydirected extremities 38 (FIG. 3) which are fixedly secured by welding orother suitable means to the armature 20 thereby constituting a unitaryarmature and armature extension.

It should be noted the armature pivot shaft 33 is not fully seatedwithin the slots 33 since the armature pivot shaft 34) engages thearmature 20 at the line 32, which line is to the left of the end of theslots 33 as shown in FIGJI. Thus, the tolerances or adjustments betweenthe depth of the slots 33 and the armature 20 at the line 32 have beeneliminated. Also, it should be noted that the rightmost portion of thearmature pivot shaft extends to the right beyond the plane of the poleface 22 as seen in FIG. 1.

To afford a compact electromagnet assembly, the armature extensions 35are made of n onmagnetic material so as not to pick up flux and carry itto the armature 20 and the extensions are extended rearwardly in thespace on either side of the coil between the coil-15 and the outer legsof the E-shaped laminations 11. The armature extensions 35 extendupwardly and outwardly to terminate in horizontal portions 40 each ofwhich have an aperture 41 therein for connection to an instrumentalityto be actuated by the electromagnet assembly 10.

To secure the armature pivot shaft 30 within its receiving slots 25 andto bias the armature to its normally open position shown in FIG. 1 thereare provided a pair of contractile armature return springs 42 securedbetween the upstanding ears 34 on the armature extensions 55 and aspring-anchoring shaft 43 carried in a pair of open ended slots 44formed in the vertically rising portions 28 of the magnet support frame26.

The armature return springs 42 are always under tension and thus serveto exert a continual force tending to pull the shaft 43 rightwardly asviewed in FIG. 1 and to pull the upper end of the ears 34 of thearmatureextensions 35 in a counterclockwise direction as viewed in FIG. 1 aboutthe armature pivot shaft 30. Since the armature 20 is attached to theinwardly turned extremities 38 (FIG. 3) of the armature extensions 35,the armature 20 is continually urged into contact with the armaturepivot shaft 30 at the line of contact 32 by the armature return springs42. Inturn, the armature pivot shaft 30 is urged to fully seat itselfwithin the receiving slots formed in the legs 28 of the magnet supportframe 26.

As shown in FIGQI, the amount of gap between the armature 20 and poleface 22 is limited by the instrumentalities (not shown) attached tothearmature extensions 35. Obviously, a stop could be provided in the pathof the armature 20 to limit its return rotation about the shaft 30. Thegap between the armature 26 and pole face 22 near the midpoint of thepole face 22 is approximately .020 of an inch and about .025 at thelower ends of the pole face 22 and armature 20.

To prevent lateral movement of. the armature pivot shaft iiti relativeto the magnet support frame 26, a pair of snap rings 45 are secured tothe armature pivot shaft, one on each side of one of the verticallyrising portions 28 of the magnet support frame 26. Similarly, topreventlateral movement of the armature extensions 35 and armature 20 relativeto the laminations 11 and the coil 15, a pair of snap rings 47 aresecured to the pivot shaft 30 and positioned on each side of one of thearmature extensions 35.

It should be appreciated that the entire assembly of laminations 11 andcoil 15, on the frame 26 with shaft 30, shaft 43 and armature 20 andarmature extensions are held together by the springs 42. Thus, themagnet assembly is readily capable of assembly and disassembly withoutthe use of the usual fasteners.

In operation, the coil 15 of electromagnet assembly It is energized andcreates a magnetic field to attract the armature 20 towards the poleface 22 on the laminations 11. During movement of the armature 20,armature extensions 35 move therewith in an arcuate manner about thearmature pivot shaft 30. The amount of movement of the armature 20 toits pole face 22 is .025 at the greatest point and at the midpoint ofthe pole face 22 is about .020 which is a small distance, and hence themagnetic force applied to the armature 20 is quite large. It should benoted that the armature 20 engages the pole face 22 only at its lowerextremity since the upper extremity of the armature is maintained at adistance from the pole face by that portion of the pivot shaft 30 whichextends outwardly beyond the pole face 22. The armature extensions 35multiply the .020 of an inch of movement of the armature 20 into a largemovement of approximately .l00 of an inch at the outer extremity of thearmature extensions 35. Upon de-energization of the coil 15, thearmature return springs 42 will act through the upstanding ears 34 ofthe armature extensions 35 to rotate the armature 20 in acounterclockwise direction, as viewed in FIG. 1, about the armaturepivot shaft 30 to return the armature 20 to the position shown inFIG. 1. In practice, it has been found that armature pivot shaft 30rotates in the receiving slots 25 over a large number of operationsthereby distributing the Wear over the entire peripheral surface of thepivot shaft 30. Any small amount of wear of the shaft 30 reduces theextent to which the shaft 30 extends over the pole face 22. With adecreasing air gap, the magnet becomes more powerful than it was with alarge air gap.

From the foregoing, it should be apparent that the mag- 7 net assemblyis an exceedingly simple structure that is readily assembled anddisassembled merely upon the disengaging of the armature return springs.Also, it should be apparent that adjustments can be eliminatedand closetolerances held by the grinding of the poleface and receiving slotssimultaneously and by having the armature urge its pivot shaft withinthe receiving-slots. Also, if any wear occurs there will be noaccompanying looseness of parts since these armature return springs urgethe armature and its pivot shaft into contact with each other and urgethe shaft into the slot 25. Finally, it should be apparent that a morecompact assembly is achieved by disposing the armature extensions withinthe space existing between the coil and laminations on each side of thecoil.

Although only one embodiment of the invention is shown in the drawingsand described in the foregoing specification, it will be understood thatinvention is not limited to the specific embodiment described, but iscapable of modification and rearrangement and substitution of parts andelements without departing from the spirit of the invention.

What is claimed is:

1. An electromagnet assembly comprising a frame, an energizable coilcarried by said frame, a plurality of metallic laminations fixed to saidframe and constituting a magnetizable core for the electromagnet, saidlaminations having their ends disposed to constitute a pole face forthe.

electromagnet, locating surfaces in said frame, an armature shaft urgedinto engagement with said locating surfaces and free for rotation withrespect thereto, an armature having at least one flat surface engagingthe periphery of said shaft in a line of contact and movable intoengagement with said pole face upon energization of the coil of themagnet, and biasing means urging said flat surface of said armatureagainst said armature shaft and thereby urging said armature shaft intoengagement with said locating surfaces in said frame whereby said shaftand said fiat surface of the armature maintain a line of contact betweenthem during operation of the armature.

2. In an electromagnet assembly having a frame means,

a coil, and laminations attached to the frame means, the improvementcomprising: i

(a) a pair of open ended bearing surfaces in said frame means,

(b) an armature shaft in engagement with said bearing surfaces,

(c) an armature urged into engagement with a portion of said armatureshaft,

(d) armature extension means secured to said armature and having slotstherein for partially encircling said armature shaft therebyconstituting with that portion of the armature in engagement with thearmature shaft, a pivot for the armature, and p (e) a springinterconnecting said frame means and said armature extension meansthereby urging said arma ture against said armature shaft to retain saidarmature shaft against said bearing surfaces.

3. The magnet assembly of claim 2 wherein a pair of open ended slots areprovided in said frame means, a spring anchoring shaft is seated withinthe slots and wherein the spring means interconnecting the armatureextension means and the frame means retains said anchoring shaft in saidslots.

4. In an electromagnet assembly having a frame to which are secured acoil and a core forming laminations and having an armature movable uponenergization of the electromagnet, the improvement comprising:

(a) a pair of open ended slots constituting location surfaces in saidframe,

(b) a pole face on said laminations spaced a predetermined distance fromsaid location surfaces,

(0) a shaft disposed in the slots in the frame and thereby having aportion of its peripheral surface accurately located with respect tosaid pole face,

(d) an armature means having a portion thereof in engagement with saidshaft thereby accurately locating said armature with respect to saidpole face,

(e) armature extension means secured to said armature and movable withsaid armature to amplify the movement of said armature means,

(1) said armature extension means having open ended slots formed thereinfor engaging said shaft at two spaced points and thereby constitutingwith said armature means a pivot for said armature means and saidarmature extension means,

(g) holding means on said frame, and

( h) armature return spring means interconnecting said holding means andsaid armature extension means thereby urging said armature means againstsaid shaft and holding said shaft in the slots and said armature meansin engagement with said shaft.

5. In the electromagnet assembly of claim 4, said laminationssurrounding said coil on at least two sides and spaced from said coil onthese two sides, said armature extensions being of nonmagnetizablematerial being disposed in this space.

References Cited in the file of this patent UNITED STATES PATENTSStevens Mar. 9, 1926 2,259,127 Eaton Oct. 14, 1941

1. AN ELECTROMAGNET ASSEMBLY COMPRISING A FRAME, AN ENERGIZABLE COILCARRIED BY SAID FRAME, A PLURALITY OF METALLIC LAMINATIONS FIXED TO SAIDFRAME AND CONSTITUTING A MAGNETIZABLE CORE FOR THE ELECTROMAGNET, SAIDLAMINATIONS HAVING THEIR ENDS DISPOSED TO CONSTITUTE A POLE FACE FOR THEELECTROMAGNET, LOCATING SURFACES IN SAID FRAME, AN ARMATURE SHAFT URGEDINTO ENGAGEMENT WITH SAID LOCATING SURFACES AND FREE FOR ROTATION WITHRESPECT THERETO, AN ARMATURE HAVING AT LEAST ONE FLAT SURFACE ENGAGINGTHE PERIPHERY OF SAID SHAFT IN A LINE OF CONTACT AND MOVABLE INTOENGAGEMENT WITH SAID POLE FACE UPON ENERGIZATION OF THE COIL OF THEMAGNET, AND BLASING MEANS URGING SAID FLAT SURFACE OF SAID ARMATUREAGAINST SAID ARMATURE SHAFT AND THEREBY URGING SAID ARMATURE SHAFT INTOENGAGEMENT WITH SAID LOCATING SURFACES IN SAID FRAME WHEREBY SAID SHAFTAND SAID FLAT SURFACE OF THE ARMATURE MAINTAIN A LINE OF CONTACT BETWEENTHEM DURING OPERATION OF THE ARMATURE.